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"What does it mean if there is blood in a blister?"
I got a blister on the back of my heel after a long hike this weekend. I decided not to pop the blister and just let it heal. Now it looks like it is filled with blood. What does this mean? Is it infected? Should I have a doctor look at it?
I would like to commend you on not popping the blister, as that is what most people chose to do, and I will tell you why I think you did the right thing. A blister typically forms from friction, or rubbing, heat (burn), or chemical exposure. They form within the outer layer of skin called the epidermis, and may present due to micro-tear's in the layers of the epidermis from the shear force of the friction. This creates a very small potential space that transudative fluid like the serum from your blood (the clear/yellow fluid that normally fills blisters) can seep into. Some think that the purpose of the fluid collection is to cushion the deeper skin from further insult from whatever caused the blister in the first place. Whether or not this is true, Assuming that the outer skin has not been violated at all, the transudative fluid within a blister should be sterile (have no bacteria in it). Thus it should not be infected. But when people "pop" them, it is not longer sterile and they can get infected. They can then be filled with pus, which would obviously be a sign of infection. Occasionally the force that created the blister in the first place can also break a very small blood vessel that bleeds into the potential space of the blister...aka a blood blister. It is nothing to worry about. Over time the blood will reabsorb, or the outer skin of the blister will slough off as the area heals and the blood will drain out. If you think that it has gotten infected, or if it starts to drain pus, I would recommend making an appointment with a family physician to get it checked out. Best of luck.
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